WSP08301

• File Number: 8273.100.50
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - BOR
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/1/1988
• Title: Estimating Economic Impacts of Salinity of the Colorado River - Final Report - February 1988
• Water Supply Pro - Doc Type: Report/Study

Economic Damages to Irrigated Agriculture 25

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baseline level below the threshold of salinity
damage from the crop in question; and the
second, the actual level that can be expected
from the USBR simulation of river conditions
(projections shown on figures 3-5, page 19).

Next, twelve crops were selected that repre-
sent the highest value crops in the irrigated
farms of the Lower Basin, and which have
salinity damage thresholds within the range of
200-1200 mgIL, as determined by E.V. Maas of
the U.S. Salinity Laboratory. The highest value
crops were identified from the most recent
(1985) Bureau of Reclamation Summary Statis-
tics, Vol. I Water, Lalld, alld Related Data. They
are: lettuce, alfalfa hay, cotton lint, wheat, sugar
beets, carrots, cantaloupe/melons,
oranges/tangerines, lemonsllimes, grapefruit,
table grapes, and dates. However, five of these
crops were excluded because their salinity
damage threshold exceeds 1200 mgiL: cotton
lint, wheat, sugar beets, dates, and cantaloupe/
melons. Two other salt-sensitive crops of rela-
tively high value were added: onions and
avocados.

Regressions on Yield of
Agricultural Crops

Data on crop yield of nine salt-sensitive
crops in three agricultural counties where
Colorado River water is used for irrigation were
obtained by year for the 1971-1984 period from
Arizona and California agricultural statistics.
The counties were Yuma, Arizona; Imperial,
California; and'Riverside, California. La paz
County, Arizona, had been created only in 1983,
so data were sparse and therefore not included.
The data show average yield of each crop in con-
ventional units of yield (e.g., tons or cwt) per
acre.

Data on salinity levels in the Colorado River
at Imperial Dam and at Parker Dam were ob-
tained for each of the years from the Bureau of
Reclamation's Quality of Water, Colorado River
Basill, Progress Report No. 13, January 1987,
Tables 19 and 20. During the 1971-1984 period,
TDS values ranged from 675 to 892 mgiL at

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Imperial Dam and from 611 to 758 mgiL at
Parker Dam.

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These data were combined into data sets
(yield vs. TDS) and regression curves and for-
mulas generated using the computer regression
program. For six of the crops, data from all
three counties were available, although Yuma
County data on citrus crop yield (i.e., oran-
ges/tangerines, grapefruit, and lemonsllimes)
were available only for tbe 1980-1984 period.
For carrots, yield data were available only for
Imperial and Riverside Counties. For avocados
and table grape,s, yield data were available only
for Riverside County.

By combining data from three counties, the
implicit hypothesis was made that salinity is the
sole factor determining yield, and that other
factors such as climate, local rainfall and
temperature variations, soil quality, and farming
techniques are uniform among the counties.
Such simplification is known to be untrue, so
the yield data being regressed against salinity are
believed to provide only an approximation of the
true yield/salinity relationship. Nevertheless, no
better data are known to be available for use in
this study.

The use of an empirical TDS/yield relation-
ship based on actual crops grown and on such
profit maximizing adjustments in agricultural
techniques as were made in the Lower Basin
during the 1971-85 period parallels the reasoning
of Richard Gardner, who calculated annual
salinity damages "as the difference in net income
between the two salinity levels, that is, the
amount by which profits are reduced after all
profit maximizing adjustments have been made
to the higher salinity level."lO

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For some crops, inspection of the data shows
that crop yields from the desert portion of River-
side County are lower than those in Imperial and
Yuma Counties, even though Riverside County
receives Colorado River water from below
Parker Dam which is less saline than water from
below Imperial Dam. Such an inversion causes
illogical regression results, e.g., that carrot yield
is directly (not inversely) proportional to salinity

lORichard L. Gardner, "Economics and Cost Sharing of Salinity Control in the Colorado River Basin," Ph.D. disserta-
tion, Agricultural and Natural Resource Economics Department, Colorado State University, Fort Collins, Fall 1983, p. 124.

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